Tactic responses of the parasitic mite, Psoroptes ovis, to light and temperature.

The astigmatid mite, Psoroptes ovis (Hering) (Acari: Psoroptidae), is an obligate, non-burrowing ectoparasite of vertebrates, of particular economic importance in domestic sheep flocks where it causes clinical psoroptic mange. To help understand the behaviour which facilitates transmission via the environment, the responses of P. ovis derived from rabbits (syn. Psoroptes cuniculi) to temperature and light were examined in the laboratory. On a vertical surface of uniform temperature, the presence and direction of illumination had a significant effect on the distance and direction moved by the mites. In darkness or with illumination from both above and below, the mites moved relatively little, but this movement was upwards. In contrast, with illumination from above only, mites moved downwards. When the direction of the illumination was reversed so that it came from below only, the mites moved upwards. On a vertical surface with a temperature gradient, in darkness or with illumination from both above and below, the mites moved up or down towards the area of highest temperature, depending on whether this was above or below, respectively. However, the movement of the mites in response to the temperature gradient was strongly displaced up or down by the presence of unidirectional illumination from above or below, respectively. The results indicate that the movement of these mites is strongly directed towards areas of high temperature but away from higher light intensity. These behaviours might be expected to maintain the position of the mites on a host animal and help them locate the skin surface of a new host when displaced into the environment.